/*
 * Copyright (c) 2009, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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package java.util;

import java.util.function.Supplier;

/**
 * This class consists of {@code static} utility methods for operating
 * on objects.  These utilities include {@code null}-safe or {@code
 * null}-tolerant methods for computing the hash code of an object,
 * returning a string for an object, and comparing two objects.
 *
 * @since 1.7
 */
public final class Objects {

  private Objects() {
    throw new AssertionError("No java.util.Objects instances for you!");
  }

  /**
   * Returns {@code true} if the arguments are equal to each other
   * and {@code false} otherwise.
   * Consequently, if both arguments are {@code null}, {@code true}
   * is returned and if exactly one argument is {@code null}, {@code
   * false} is returned.  Otherwise, equality is determined by using
   * the {@link Object#equals equals} method of the first
   * argument.
   *
   * @param a an object
   * @param b an object to be compared with {@code a} for equality
   * @return {@code true} if the arguments are equal to each other and {@code false} otherwise
   * @see Object#equals(Object)
   */
  public static boolean equals(Object a, Object b) {
    return (a == b) || (a != null && a.equals(b));
  }

  /**
   * Returns {@code true} if the arguments are deeply equal to each other
   * and {@code false} otherwise.
   *
   * Two {@code null} values are deeply equal.  If both arguments are
   * arrays, the algorithm in {@link Arrays#deepEquals(Object[],
   * Object[]) Arrays.deepEquals} is used to determine equality.
   * Otherwise, equality is determined by using the {@link
   * Object#equals equals} method of the first argument.
   *
   * @param a an object
   * @param b an object to be compared with {@code a} for deep equality
   * @return {@code true} if the arguments are deeply equal to each other and {@code false}
   * otherwise
   * @see Arrays#deepEquals(Object[], Object[])
   * @see Objects#equals(Object, Object)
   */
  public static boolean deepEquals(Object a, Object b) {
    if (a == b) {
      return true;
    } else if (a == null || b == null) {
      return false;
    } else {
      return Arrays.deepEquals0(a, b);
    }
  }

  /**
   * Returns the hash code of a non-{@code null} argument and 0 for
   * a {@code null} argument.
   *
   * @param o an object
   * @return the hash code of a non-{@code null} argument and 0 for a {@code null} argument
   * @see Object#hashCode
   */
  public static int hashCode(Object o) {
    return o != null ? o.hashCode() : 0;
  }

  /**
   * Generates a hash code for a sequence of input values. The hash
   * code is generated as if all the input values were placed into an
   * array, and that array were hashed by calling {@link
   * Arrays#hashCode(Object[])}.
   *
   * <p>This method is useful for implementing {@link
   * Object#hashCode()} on objects containing multiple fields. For
   * example, if an object that has three fields, {@code x}, {@code
   * y}, and {@code z}, one could write:
   *
   * <blockquote><pre>
   * &#064;Override public int hashCode() {
   *     return Objects.hash(x, y, z);
   * }
   * </pre></blockquote>
   *
   * <b>Warning: When a single object reference is supplied, the returned
   * value does not equal the hash code of that object reference.</b> This
   * value can be computed by calling {@link #hashCode(Object)}.
   *
   * @param values the values to be hashed
   * @return a hash value of the sequence of input values
   * @see Arrays#hashCode(Object[])
   * @see List#hashCode
   */
  public static int hash(Object... values) {
    return Arrays.hashCode(values);
  }

  /**
   * Returns the result of calling {@code toString} for a non-{@code
   * null} argument and {@code "null"} for a {@code null} argument.
   *
   * @param o an object
   * @return the result of calling {@code toString} for a non-{@code null} argument and {@code
   * "null"} for a {@code null} argument
   * @see Object#toString
   * @see String#valueOf(Object)
   */
  public static String toString(Object o) {
    return String.valueOf(o);
  }

  /**
   * Returns the result of calling {@code toString} on the first
   * argument if the first argument is not {@code null} and returns
   * the second argument otherwise.
   *
   * @param o an object
   * @param nullDefault string to return if the first argument is {@code null}
   * @return the result of calling {@code toString} on the first argument if it is not {@code null}
   * and the second argument otherwise.
   * @see Objects#toString(Object)
   */
  public static String toString(Object o, String nullDefault) {
    return (o != null) ? o.toString() : nullDefault;
  }

  /**
   * Returns 0 if the arguments are identical and {@code
   * c.compare(a, b)} otherwise.
   * Consequently, if both arguments are {@code null} 0
   * is returned.
   *
   * <p>Note that if one of the arguments is {@code null}, a {@code
   * NullPointerException} may or may not be thrown depending on
   * what ordering policy, if any, the {@link Comparator Comparator}
   * chooses to have for {@code null} values.
   *
   * @param <T> the type of the objects being compared
   * @param a an object
   * @param b an object to be compared with {@code a}
   * @param c the {@code Comparator} to compare the first two arguments
   * @return 0 if the arguments are identical and {@code c.compare(a, b)} otherwise.
   * @see Comparable
   * @see Comparator
   */
  public static <T> int compare(T a, T b, Comparator<? super T> c) {
    return (a == b) ? 0 : c.compare(a, b);
  }

  /**
   * Checks that the specified object reference is not {@code null}. This
   * method is designed primarily for doing parameter validation in methods
   * and constructors, as demonstrated below:
   * <blockquote><pre>
   * public Foo(Bar bar) {
   *     this.bar = Objects.requireNonNull(bar);
   * }
   * </pre></blockquote>
   *
   * @param obj the object reference to check for nullity
   * @param <T> the type of the reference
   * @return {@code obj} if not {@code null}
   * @throws NullPointerException if {@code obj} is {@code null}
   */
  public static <T> T requireNonNull(T obj) {
    if (obj == null) {
      throw new NullPointerException();
    }
    return obj;
  }

  /**
   * Checks that the specified object reference is not {@code null} and
   * throws a customized {@link NullPointerException} if it is. This method
   * is designed primarily for doing parameter validation in methods and
   * constructors with multiple parameters, as demonstrated below:
   * <blockquote><pre>
   * public Foo(Bar bar, Baz baz) {
   *     this.bar = Objects.requireNonNull(bar, "bar must not be null");
   *     this.baz = Objects.requireNonNull(baz, "baz must not be null");
   * }
   * </pre></blockquote>
   *
   * @param obj the object reference to check for nullity
   * @param message detail message to be used in the event that a {@code NullPointerException} is
   * thrown
   * @param <T> the type of the reference
   * @return {@code obj} if not {@code null}
   * @throws NullPointerException if {@code obj} is {@code null}
   */
  public static <T> T requireNonNull(T obj, String message) {
    if (obj == null) {
      throw new NullPointerException(message);
    }
    return obj;
  }

  /**
   * Returns {@code true} if the provided reference is {@code null} otherwise
   * returns {@code false}.
   *
   * @param obj a reference to be checked against {@code null}
   * @return {@code true} if the provided reference is {@code null} otherwise {@code false}
   * @apiNote This method exists to be used as a {@link java.util.function.Predicate}, {@code
   * filter(Objects::isNull)}
   * @see java.util.function.Predicate
   * @since 1.8
   */
  public static boolean isNull(Object obj) {
    return obj == null;
  }

  /**
   * Returns {@code true} if the provided reference is non-{@code null}
   * otherwise returns {@code false}.
   *
   * @param obj a reference to be checked against {@code null}
   * @return {@code true} if the provided reference is non-{@code null} otherwise {@code false}
   * @apiNote This method exists to be used as a {@link java.util.function.Predicate}, {@code
   * filter(Objects::nonNull)}
   * @see java.util.function.Predicate
   * @since 1.8
   */
  public static boolean nonNull(Object obj) {
    return obj != null;
  }

  /**
   * Checks that the specified object reference is not {@code null} and
   * throws a customized {@link NullPointerException} if it is.
   *
   * <p>Unlike the method {@link #requireNonNull(Object, String)},
   * this method allows creation of the message to be deferred until
   * after the null check is made. While this may confer a
   * performance advantage in the non-null case, when deciding to
   * call this method care should be taken that the costs of
   * creating the message supplier are less than the cost of just
   * creating the string message directly.
   *
   * @param obj the object reference to check for nullity
   * @param messageSupplier supplier of the detail message to be used in the event that a {@code
   * NullPointerException} is thrown
   * @param <T> the type of the reference
   * @return {@code obj} if not {@code null}
   * @throws NullPointerException if {@code obj} is {@code null}
   * @since 1.8
   */
  public static <T> T requireNonNull(T obj, Supplier<String> messageSupplier) {
    if (obj == null) {
      throw new NullPointerException(messageSupplier.get());
    }
    return obj;
  }
}
